1. Field of the Invention:
The invention relates to lawn trimmers of the type utilizing flexible strands rotated at high speed as the cutting element. In particular, the invention relates to cordless electric lawn edgers having a detachable and disposable tip for retaining the strand and positioning the strand in an operative cutting position.
2. Description of the Prior Art:
It is well known that conventional wide-swath lawn mowers (e.g., 16 to 36 inches) are unable to cut grass and weeds near trees and buildings and adjacent sidewalks. Thus, the homeowner must trim these areas by other means in order to maintain a neat lawn. Edgers for this task have included hand-operated scissorlike trimmers as well as portable cordless electric shears such as disclosed in U.S. Pat. No. 3,623,223.
It has long been known that non-woody vegetable tissues may be cut or separated by striking them rapidly with edges of planar objects such as sickles and scythes. If the speed is sufficiently high, fairly blunt edges such as those found on rotary lawn mowers may be used. Recently, it has been determined that a blunt flexible cord or strand could be used to effect such cutting. This principle has been applied in the lawn edging art whereby a flexible filament or strand is rotated to effect cutting. With such rotating strand devices, most of the cutting is done near the tips of the strands where the speed is highest. Patents illustrative of such flexible filament lawn edgers include U.S. Pat. Nos. 3,708,967; 3,831,278; 3,892,037 and 3,895,440.
A major obstacle encountered with prior art strand lawn edgers is the replacement of the strand when it becomes worn due to contact with trees, concrete, or the like. One approach has been to provide a supply of filament within the device and continually feeding or "paying out" the line as it is shortened through wear. This solution not only involves complicated and costly filament feed apparatus, but also has the added disadvantage of always presenting a worn or frayed filament end for cutting. Since most of the cutting takes place at the end of the strand where the speed is highest, the frayed strand may greatly decrease the cutting efficiency.
Other filament edgers, such as the edger described in U.S. Pat. No. 3,831,278, utilize a single strand length secured at its center to a rotating member. Two analogous devices are found in U.S. Pat. Nos. 2,663,137 and 3,018,602 wherein wires are secured between parallel rotating plate members to hold the wires in place for cutting. However, these patented devices do not provide a simple means for replacing the strands or wires when they are worn or frayed.
U.S. Pat. Nos. 3,670,413 and 3,877,146 are illustrative of coupling arrangements between rotatable blades and their motor shafts. The groove approach in U.S. Pat. No. 3,670,413 allows slippage of the blade relative to the motor shaft and would be detrimental to the functioning of the tool of this invention.
Prior to the present invention, applicants were aware of no commercially available cordless electric strand cutting device. This is due primarily to the fact that the prior art devices have high power requirements not compatible with a rechargeable battery power source. The motors of the known devices generally must rotate a relatively high mass which in some cases includes a supply of line that is payed out as the line wears. In other cases, the power requirements are increased because of the drag produced between the rotating elements and the grass as well as a tendency for the grass to wrap around such elements. Because of the availability of relatively high power AC motors for use on the AC trimmers of the prior art, the designers of such trimmers have not adequately dealt with the problem of reducing power drain.
Thus, it becomes an object of the present invention to provide a cordless electric flexible strand cutting device having a rotating strand mounting assembly which places a minimum load on the DC motor so as to be compatible with a rechargeable battery source of power and adapted to being plastic molded.
Another object of the invention is to provide a simple and inexpensive means for assuring that a fresh and unfrayed strand is always exposed for maximum cutting efficiency. In particular, it becomes an object to provide a detachable and disposable tip member incorporating a cutting strand and which may be easily replaced when the strand becomes shortened or frayed due to wear.
Another object of the invention is to provide an upright cordless electric strand lawn edger having both a grip handle and a loop handle positioned for optimum tool balance and handling.